The present invention relates to printers. Furthermore, the present invention relates to an inkjet delivery system that conditions the ink prior to printing.
Printers are used to print output from computers or similar type of devices that generate information, onto a recording medium such as paper. Commonly available types of printers include impact printers, laser printers and inkjet printers. The term “inkjet” covers a variety of physical processes and hardware but basically these printers transfer ink from an ink supply to the recording medium in a pattern of fine ink drops. Inkjet printheads produce drops either continuously or on demand. “Continuously” means that a continuous stream of ink drops is created, e.g. by pressurizing the ink supply. Typically, continuous inkjet printing utilizes a pump to cause ink to be transmitted from a reservoir through a gunbody and nozzle in accordance with Plateau-Rayleigh instability.
“On demand” inkjet printing differs from “continuous” inkjet printing in that ink drops are only ejected from a printhead by manipulation of a physical process to momentarily overcome surface tension forces that keep the ink in the printhead. The ink is held in a nozzle, forming a meniscus. The ink remains in place unless some other force overcomes the surface tension forces that are inherent in the liquid. The most common practice is to suddenly raise the pressure on the ink, ejecting it from the nozzle. One category of drop-on-demand inkjet printheads uses the physical phenomenon of electrostriction, a change in transducer dimension in response to an applied electric field. Electrostriction is strongest in piezoelectric materials and hence these printheads are referred to as piezoelectric printheads. The very small dimensional change of piezoelectric material is harnessed over a large area to generate a volume change that is large enough to squeeze out a drop of ink from a small chamber. A piezoelectric printhead includes a multitude of small ink chambers, arranged in an array, each having an individual nozzle and a percentage of transformable wall area to create the volume changes required to eject an ink drop from the nozzle, in according with electrostriction principles.
For production type inkjet printing equipment, where high printing speeds and reliability are of the outmost importance, the conditioning of the ink is critical. The solutions proposed in the prior art only partially solve some of the problems.
Inkjet printers are prone to head nozzle clogging because of the small nozzle size and the use of water based inks. To remedy this, prior methods are to fire all the piezo elements to pump ink through the head or apply a vacuum to the printhead through a capping device. These methods have limited success because they can only apply relatively low pressure to the nozzles.
In addition, in printing where white ink is used, the titanium oxide pigment tends to come out of suspension from the vehicle used. To remedy this, conditioning by agitation or stirring is needed. Prior methods are to fire all the piezo elements to pump ink through the head or apply a vacuum to the printhead through a capping device which wastes ink. Colored inks may also benefit from conditioning by agitation or stirring.
Therefore, there is a significant need to provide an ink delivery system, incorporated in an inkjet printer, that brings the ink in optimal condition immediately after startup and keeps it in optimal condition during printing.